Technical Field
The present invention relates to a device for decontaminating surfaces by hydroblasting enabling a removal of toxic products, and more particularly asbestos and lead, with almost no emission of contaminated particles in the atmosphere in order to ensure worker safety, reduce the onerousness of workers and protect the direct environment, that is to say the decontamination area demarcating the site, and the indirect environment, that is to say, the environment around the decontamination site.
Prior Art
Asbestos has been known for over two thousand years and has long been used in a number of materials and products, due to its acoustic and thermal insulation properties, resistance to heat and fire, chemical inertness, mechanical strength and rot-proof properties. However, the physicochemical characteristics of asbestos, in combination with an ability to splinter into split microscopic fibres to reach the pulmonary alveoli, and even migrate to the pleura, result in significant inhalation of asbestos fibres becoming hazardous. According to the regulation, a worker must not inhale more than 0.1 fibres per cm3 in an hour. Pathologies, mainly lung cancer, can manifest themselves for more than fifty years after the first exposure to asbestos fibres. The adverse effects on human health have therefore led to a control and then a gradual reduction of its use, followed by total prohibition since 1 Jan. 1997, by decree no. 96-1133 of 24 Dec. 1996 on the prohibition of asbestos, adopted under the Labour Code and the Consumer Code.
Currently, asbestos removal operations are carried out in multiple restrictive steps, as they must meet safety standards both for the worker and the environment. The worker must be provided with overalls and a respiratory system in order to avoid inhaling loose asbestos dust, which can be extremely toxic. His work must be performed in an enclosed area with access to said zone through an airlock, divided into several compartments, including two shower areas. This enclosed area must have a lower air pressure than the outside air so that in case of leakage, it is the outside air that enters the enclosed area, and not vice versa. This enclosed area is formed using two polyane films that the protect surfaces that are not subject to asbestos removal. A proper ventilation system must also be provided.
However, it is common that the overalls and/or the respiratory system become inoperative during the site work, due to a tear in the overalls or a malfunction of the respiratory system, for example, such that the workers breathe more than 0.1 fibres per cm3 for an hour exposing themselves to fatal diseases. Moreover, despite all the precautions taken during the confinement, since the said confinement requires a long time for setting up, and the mandatory checks that significantly increase the cost of asbestos removal sites, asbestos fibres can escape from the confinement area thereby endangering persons outside the site, who are likely to unknowingly breathe asbestos fibres.
The asbestos thus removed from its support can undergo treatment that renders it inert, that is to say, changes it to make it non-toxic to humans. This treatment can consist of vitrification, as described in patents FR 2 853 846 and FR 2 690 093, where the asbestos waste is incorporated in a special furnace to reach very high temperatures. The waste may be packed beforehand, for example by prior bagging, as described in patent FR 2 746 037.
However, it is during the removal of asbestos from its support that the inhalation risks are the greatest. In this regard, it is common to use scrapers and/or sanders to release the asbestos from its support, which produces a large amount of asbestos dust, which may spread in the ambient air. The common methods of asbestos removal require draconian safety conditions without, however, detoxifying the product.
Many alternatives have been found to enable one-step waste removal while rendering the waste inert. This is particularly the case of the U.S. Pat. No. 4,693,755 which describes a method of removing asbestos from its support after the application of a cellulosic polymer-based composition that penetrates and dries the asbestos dust to make it inert.
However, this type of process is no longer used in view of the chemical risks it creates for workers and the environment.
Also known is the patent FR 2 875 720 which describes an asbestos removal method using cold conditions. Following the injection of liquid nitrogen, at a temperature between −40° C. and −196° C., the asbestos freezes into its support and can be removed safely.
Besides the high cost of liquid nitrogen, this process requires an additional step of processing asbestos fibres, which increases the cost of the jobsite.
Also known is the document FR 2 815 276 which describes a device for removal of asbestos from surfaces comprising an apparatus for projection of a high pressure liquid jet, the said pressure being between 1000 and 2000 bars, at a distance of about one meter from the surface to be treated, separate pumping means for drawing the wet residue resulting from the decomposition of the coating fallen on the ground, a filtration system consisting of a filtering press and, optionally, a second filtration system.
All these methods and devices implementing these processes have the disadvantage, in addition to being costly, of producing a very high quantity of asbestos dust which poses a highly significant risk to workers and the environment. In addition, decree no. 2012-639 requires that, from 1 Jul. 2015, the average concentration of asbestos fibres in eight hours of work shall not exceed ten fibres per liter. Therefore, this is one-tenth of the previously authorised rate which placed the limit to 100 fibres per liter. Three classification categories have thus been implemented. At the “first level”, the dust cover is lower than the occupational exposure limit value (OELV). At the “second level”, the value is greater than or equal to the OELV and less than 60 times the OELV. Finally at the “third level”, the value is greater than or equal to 60 times the OELV and less than 250 times the OELV. Thus, immediate consequence of this reduction of the occupational exposure limit value (OELV) will be an increase in cost of the asbestos removal operations using asbestos removal methods of the prior art.
Furthermore, in buildings, there are other products that may constitute a health hazard and that must be safely removed to protect the health of workers particularly during dismantling operations. This is particularly the case of lead, which may cause lead poisoning and is found in many surface coatings such as old paint, PCBs (polychlorinated biphenyls) that are chemicals similar to dioxin found in expansion joints and in some coatings, polycyclic aromatic hydrocarbons (PAHs) that are persistent organic pollutants present in products made from bitumen such as road paving, bituminous adhesives, vapour barriers, sealing materials, walls of treatment plants, walls of water towers, etc., and radioactive products found in cooling towers, containment vessels of reactors of nuclear power plants.
There is therefore a need for a method and a device that can be used for surface treatment comprising one or more toxic products which help remove said products with complete safety for workers and the environment.